As an electrophotographic photoreceptor, there has recently come to be known an organic photoreceptor having a good processability, an advantage in manufacturing cost, and a large degree of freedom in function designing. However, an organic photoreceptor developed in the early stage was not satisfactory in sensitivity and durability; therefore, there was developed an electrophotographic photoreceptor of function-separating type in which the carrier generation function and carrier transfer function are separately provided by different substances. Such an electrophotographic photoreceptor has an advantage that materials having appropriate characteristics can be selected from a wide range of compounds. This makes it possible to develop an organic photoreceptor of high sensitivity and high durability.
As carrier generation materials and carrier transfer materials, a variety of organic compounds are proposed; particularly, carrier generation materials have an important function to control fundamental characteristics of a photoreceptor. And as such carrier generation materials, there have so far been known polycyclic quinone compounds, perylene compounds, phthalocyanine compounds and azo compounds.
Electrophotographic photoreceptors using perylene compounds as a carrier generation material are disclosed, for example, in Japanese Pat. Exam. Pub. No. 8423/1986, Japanese Pat. O.P.I. Pub. Nos. 59686/1984, 180956/1988 and 291061/1988. But the perylene compounds used in those techniques are insufficient in color sensitivity, especially in red color reproduction, when used as a photoreceptor for plain paper copiers, because of their spectral sensitivities limited to 400 to 750 nm. Though there have also been proposed electrophotographic photoreceptors using a polycyclic quinone compound jointly with an azo compound or a phthalocyanine compound as a carrier generation material, these are not necessarily stable in repeatabilities of sensitivity, electrification potential and residual potential. Therefore, when these are used as positive electrification photoreceptors, the electrification potential is noticeably lowered by repeated use, and when images are formed with such a copier using the photoreceptors, white spots due to poor dispersion of carrier generation material are liable to occur.
The present invention is accomplished to solve the above problems. Accordingly, the object of the invention is to provide an electrophotographic photoreceptor excellent in spectral sensitivity, high in sensitivity and durability, free from lowering of electrification potential by repeated use, and thereby capable of preventing image defects.